Xiaomi never followed up the Poco F1 with a Poco F2. It appears, however, that the company actually built a Poco F2 but just never released it, and a working prototype of the device has now been revealed, two years after it would've launched.
https://www.notebookcheck.net/Leaked-Poco-F2-prototype-showcases-a-phone-that-would-have-succeeded-the-Poco-F1.556000.0.html